package leetcode;

/**
 * Created by tiang on 2018/8/10.
 * N couples sit in 2N seats arranged in a row and want to hold hands. We want to know the minimum number
 * of swaps so that every couple is sitting side by side. A swap consists of choosing any two people,
 * then they stand up and switch seats.

 The people and seats are represented by an integer from 0 to 2N-1, the couples are numbered in order,
 the first couple being (0, 1), the second couple being (2, 3), and so on with the last couple being (2N-2, 2N-1).

 The couples' initial seating is given by row[i] being the value of the person
 who is initially sitting in the i-th seat.

 Example 1:

 Input: row = [0, 2, 1, 3]
 Output: 1
 Explanation: We only need to swap the second (row[1]) and third (row[2]) person.
 Example 2:

 Input: row = [3, 2, 0, 1]
 Output: 0
 Explanation: All couples are already seated side by side.
 Note:

 len(row) is even and in the range of [4, 60].
 row is guaranteed to be a permutation of 0...len(row)-1.
 */
public class CouplesHoldingHands {
    /**
     * 找到一个不匹配的之后，向后寻找一个匹配的数字与之替换
     * @param row
     * @return
     */
    public static int minSwapsCouples(int[] row) {
        int count = 0;
        for(int i=0;i<row.length;i+=2){
            int bigIndex = row[i]>row[i+1]?i:i+1;
            int big = row[bigIndex];
            int smallIndex = row[i]>row[i+1]?i+1:i;
            int small = row[smallIndex];
            if(big - small == 1 && small % 2 == 0)
                continue;
            int aimNum, aimIndex, old;
            if(small%2==0){
                aimNum = small+1;
                aimIndex = bigIndex;
                old = big;
            }else if(big %2 == 0){
                aimNum = big+1;
                aimIndex = smallIndex;
                old = small;
            }else{
                aimNum = big-1;
                aimIndex = smallIndex;
                old = small;
            }
            for(int j=i+2;j<row.length;j++){
                if(row[j] == aimNum){
                    int temp = old;
                    row[aimIndex] = row[j];
                    row[j] = temp;
                    count++;
                    break;
                }
            }
        }
        return count;
    }
}
